Over-voltage protection in a high-swing amplifier

Abstract

A method for processing signals may include comparing an output voltage signal in an output stage of an amplifier with a reference voltage signal. If the output voltage signal is greater than the reference voltage signal, a comparator voltage signal may be generated. Bias voltage for at least one output stage transistor may be increased by increasing current generated by a first bias current source of the at least one output stage transistor. The current may be increased in proportion to the generated comparator voltage signal. The output voltage signal may be divided prior to the comparing. The at least one output stage transistor may be dynamically biased based on the generated comparator voltage signal. The comparator voltage signal may be generated using at least one differential pair with a current mirror load.

What is claimed is: 
     
       1. A method comprising:
 comparing an output voltage signal in an output stage of an amplifier with a reference voltage signal; 
 generating a comparator voltage signal, if the output voltage signal is greater than the reference voltage signal; and 
 increasing bias voltage for at least one output stage transistor by increasing current generated by a first bias current source of the at least one output stage transistor, in proportion to the generated comparator voltage signal, 
 wherein the bias voltage for the at least one output stage transistor comprises a fixed voltage component and a variable voltage component. 
 
     
     
       2. The method according to  claim 1 , comprising dividing the output voltage signal prior to the comparing. 
     
     
       3. The method according to  claim 1 , comprising dynamically biasing the at least one output stage transistor based on the generated comparator voltage signal. 
     
     
       4. The method according to  claim 1 , comprising:
 generating the comparator voltage signal using at least one differential pair with a current mirror load. 
 
     
     
       5. The method according to  claim 1 , comprising:
 generating the fixed voltage component using a fixed resistor load and a second bias current source of the at least one output stage transistor. 
 
     
     
       6. The method according to  claim 5 , comprising:
 increasing the bias voltage for the at least one output stage transistor by overdriving the variable voltage component of the bias voltage. 
 
     
     
       7. The method according to  claim 6 , wherein the overdriving comprises:
 increasing the current generated by the first bias current source of the at least one output stage transistor, wherein the current passes through a replica diode of the at least one output stage transistor and a second fixed resistor load. 
 
     
     
       8. A method comprising:
 comparing an output voltage signal in an output stage of an amplifier with a reference voltage signal; 
 generating a comparator voltage signal, if the output voltage signal is less than the reference voltage signal; and 
 decreasing bias voltage for at least one output stage transistor by increasing current generated by a first bias current source of the at least one output stage transistor, in proportion to the generated comparator voltage signal, 
 wherein the bias voltage for the at least one output stage transistor comprises a fixed voltage component and a variable voltage component. 
 
     
     
       9. The method according to  claim 8 , comprising dividing the output voltage signal prior to the comparing. 
     
     
       10. The method according to  claim 8 , comprising dynamically biasing the at least one output stage transistor based on the generated comparator voltage signal. 
     
     
       11. The method according to  claim 8 , comprising:
 generating the comparator voltage signal using at least one differential pair with a current mirror load. 
 
     
     
       12. The method according to  claim 8 , comprising:
 generating the fixed voltage component using a fixed resistor load and a second bias current source of the at least one output stage transistor. 
 
     
     
       13. The method according to  claim 12 , comprising:
 decreasing the bias voltage for the at least one output stage transistor by overdriving the variable voltage component of the bias voltage. 
 
     
     
       14. The method according to  claim 13 , wherein the overdriving comprises:
 increasing the current generated by the first bias current source of the at least one output stage transistor, wherein the current passes through a replica diode of the at least one output stage transistor and a second fixed resistor load. 
 
     
     
       15. An over-voltage protection circuit, comprising:
 a divider that is operable to divide an output voltage signal in an output stage of an amplifier to generate a divided output voltage signal; 
 a comparator that is operable to compare the divided output voltage signal in with a reference voltage signal to generate a comparator voltage signal; and 
 a first bias current source coupled to the comparator and at least one output stage transistor, wherein:
 the first bias current source is operable to increase bias voltage, if the divided output voltage signal is greater than the reference voltage signal, for the at least one output stage transistor by increasing current in proportion to the generated comparator voltage signal, 
 
 wherein the bias voltage for the at least one output stage transistor comprises a fixed voltage component and a variable voltage component. 
 
     
     
       16. The over-voltage protection circuit according to  claim 15 , comprising:
 a second bias current source of the at least one output stage transistor, the second bias current source operable to generate the fixed voltage component using a first fixed resistor load. 
 
     
     
       17. The over-voltage protection circuit according to  claim 16 , comprising:
 a replica diode coupled to a second fixed resistor load, wherein the first bias current source is operable to increasing the bias voltage for the at least one output stage transistor by increasing the current passing through the replica diode and the second fixed resistor load.